Pex al pex sizing

I installed a keystoker k6 boiler in an addition last fall, and ran 3 zones in the addition using 3/4 pex al pex with compression fittings. They are all fairly large zones, and a fair distance from the boiler. I now need to run 2 small zones into the original part of my home. Neither are long loops from the boiler, probably less than 50 feet each. And it could all be one zone easily, but two zones makes planning a lot easier and I have the space. One zone will have two 8' fin tube baseboards with the return inside the enclosure. The other zone will have two small pieces of slant fin baseboard, probably 3' or so each, and it will return through the enclosure on one baseboard. I am wondering if anyone has ran smaller runs to baseboard with 1/2 inch pex Al pex. I would like to use 1/2 if I could because of the returns, and where I need to snake some lines. I want to make sure I can get enough volume with 1/2 though.

To avoid velocity noise and potential circulator 'head' issues I would go with 3/4". That said, individual zones typically only need 1.5 gpm to perhaps as high as 2.5 gpm flow if achieving a 20 degree F. drop. These flow values in conjunction wih a 20 degree drop across the loop would represent 15,000 to 25,000 BTUH delivered per zone loop respectively.

Iv seen large cast iron radiators supplied with 1/2 pipe which worked fine. So if i had the room id use 3/4 ,if not id use 1/2 . Its all about the pump, only gravity systems needs huge feed and return lines in order to work.

180 degree water at 2.7 GPM is flowing through 1/2" PEX at the rate of 8 ft/sec.

8 ft/sec is where you can hear the water flowing in the pipe.

http://www.pexuniverse.com/sites/defaul ... insert.jpg

I don't use pex compression fittings myself.

Pex is great stuff. I use the standard adapter and crimp rings.

https://i.pinimg.com/736x/b1/8d/e0/b18d ... -tools.jpg

I try to shy away from the compression unions that are just push in and prefer to use the ring-crimped variety. But I have used the push-in unions on occasion.

https://images-na.ssl-images-amazon.com ... SY355_.jpg

For radiators? I would use 3/4" myself.

Copper v. pex for this application? I think I would prefer copper but pex is approved almost everywhere. I just don't know how pex flexes under heat (copper isn't going to "kink" up at a turn). But I have done 3 bathroom renovations and used pex everywhere .. but relatively small runs (6 ft max per pex tubing) of it in the bathroom.

And I have a low pH water source that I need to treat right after it comes into the house. So pex is perfect in this environment. How many pinhole leaks have I fixed? I'm an expert at it LOL.

davidmcbeth3 wrote: ↑

Mon. Oct. 02, 2017 3:05 pm

http://www.pexuniverse.com/sites/defaul ... insert.jpg

I don't use pex compression fittings myself.

Pex is great stuff. I use the standard adapter and crimp rings.

https://i.pinimg.com/736x/b1/8d/e0/b18d ... -tools.jpg

I try to shy away from the compression unions that are just push in and prefer to use the ring-crimped variety. But I have used the push-in unions on occasion.

https://images-na.ssl-images-amazon.com ... SY355_.jpg

For radiators? I would use 3/4" myself.

Copper v. pex for this application? I think I would prefer copper but pex is approved almost everywhere. I just don't know how pex flexes under heat (copper isn't going to "kink" up at a turn). But I have done 3 bathroom renovations and used pex everywhere .. but relatively small runs (6 ft max per pex tubing) of it in the bathroom.

And I have a low pH water source that I need to treat right after it comes into the house. So pex is perfect in this environment. How many pinhole leaks have I fixed? I'm an expert at it LOL.

Pex AL pex is not the same OD and ID as normal pex, hence you have to use the compression fittings specifically for pex AL pex.

http://www.pexuniverse.com/differences- ... pex-tubing

Did not notice the "AL"

above is link showing differences

Yes, I have done what you are proposing, except I used regular oxygen barrier 1/2" pex instead of the pex-AL-pex product. Your baseboards are short enough that 1/2" will be fine.

I should also note that every zone has its own circulator on the supply side. I used grundfos ups15-58fc 1/25 hp 3 speed circulators and will also likely use them on the new zones as well if that makes any difference.